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Calcimator

Eyepiece Collection Calculator

Plan a 3-eyepiece set for your telescope with low, medium, and high power focal lengths.

Inputs

Results

Low Power Eyepiece

40 mm

Medium Power Eyepiece

15.5 mm

High Power Eyepiece

6 mm

True FOV (low power)2°
How to Use This Calculator
  1. Enter Scope Focal Length (mm), Scope f/ratio, and Min Usable Magnification.
  2. Set Max Usable Magnification.
  3. Review Low Power Eyepiece (mm), Medium Power Eyepiece (mm), and High Power Eyepiece (mm).
  4. Use True FOV (low power) (°) to inform your decision.
  5. Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Scope Focal Length (mm)

Scope Focal Length (mm)Low Power EyepieceMedium Power EyepieceHigh Power Eyepiece
1,09036.3 mm14.1 mm5.5 mm
3,565118.8 mm46 mm17.8 mm
6,535217.8 mm84.4 mm32.7 mm
9,010300.3 mm116.3 mm45.1 mm

What each input means

Scope Focal Length (mm)
Focal length of your telescope in millimeters
Scope f/ratio
f/ratio of your telescope (focal length / aperture)
Min Usable Magnification
Lowest useful magnification (rule of thumb: aperture in mm / 7)
Max Usable Magnification
Highest useful magnification (rule of thumb: aperture in mm × 2)

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Scope Focal Length (mm) = 1200, Scope f/ratio = 6, Min Usable Magnification = 30, Max Usable Magnification = 200 = 4 input(s) provided
  2. Calculate Low Power Eyepiece
    Low Power Eyepiece
    40 = 40
  3. Calculate Medium Power Eyepiece
    Medium Power Eyepiece
    15.5 = 15.5
  4. Calculate High Power Eyepiece
    High Power Eyepiece
    6 = 6

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